Bushing cap



y 1942- A. A. SKVORTZOFF BUSHING CAP Filed Feb. 18, 1941 I a u ATTORNEYWITNESSES:

Patented May 5, 1942 UNITED STAT BUSHING CAP Alexander A. Skvortzoff,Sharon, Pa., asslgnor to Westinghouse Electric & Manufacturing Company,East Pittsburgh, Pa., a. corporation of PennsylvaniaApplication'February 18, 1941, Serial No. 379,481

4 Claims.

The present invention relates to bushings for insulating the highpotential leads to electrical apparatus such as transformers and circuitbreakers, and it has particular relation to an improved cap forsealing'the exposed ends of such bushings.

Apparatus of the type contemplated generally includes a tubular casingof dielectric material such as porcelain through which extends aconducting member which may be in the form of a metallic stud or tube.In such apparatus the lower end of the casing is generally fixedrelative to the stud and a metallic cap member is disposed at the upperend to close the interior of the bushing against the entrance of outsideatmosphere and impurities which may be carried thereby.

Due to differences in the expansion properties of the casing and stud inresponse to temperature changes, it is necessary to provide a capstructure such that no dangerous stresses will be imposed upon thecasing during contraction. of the stud and all of the sealed joints willbe maintained closed during the expansion thereof.

According to the present invention, a metallic cap which is provided toclose the bushing is rigidly secured to the stud at its top and has an 4open bottom. A flexible diaphragm is secured to to the bottom of thiscap and arranged to completely seal the space between the cap and thecasing irrespective of any relative movement which may occur as a resultoi. temperature changes.

It is, accordingly, an object of the present invention to provide anovel and improved high potential insulating bushing.

It is another object of the invention to provide an insulating bushingwith a cap structure which is inexpensive to manufacture, easy toassemble and dismantle, and particularly satisfactory in operation.

Still another object of the invention is to provide an insulatingbushingcap which may be rigidly supported from the bushing stud and yetincludes a flexible metallic diaphragm for closing the insulating casingirrespective of any relative movement between the parts.

A further object of the invention is to provide a bushing of the abovetype whichmaybe tested without the necessity of disconnecting an insideterminal of the conductor from the electrical apparatus withwhich thebushing is being employed.

Other objects'and advantages of the invention will appear from thefollowing; detailed descripill tion read in conjunction with theaccompanying drawing, in which:

Figure 1 is a vertical sectional view of an insulating bushing embodyingthe present invention;

Fig. 2 is a reduced scale horizontal sectional view of a portion of thisapparatus taken along the line ill-II of Fig. 1; and

} Fig. 3 is a portion of a similar view of a modification of theinvention.

Referring to Fig. 1, the apparatus includes a tubular casing 2 which maybe of porcelain or some other suitable insulating material, and which isequipped with the usual surface creepage flanges indicated at i. Ametallic stud it extends axially through this casing and projects beyondits end as indicated in the drawing. The stud 5 may be solid as shown orin the form of a copper tube, in each of which cases it may serve as thelead conductor. it will also appear that the stud need not necessarilyserve as the conductor, but may include a fished through lead of usualtype for this purpose.

A condenser member 8 which may be built up of alternate layers ofconductor and dielectric material in a manner well known in the art ispreferably disposed about the stud within the casing. It will beunderstood that a usual type oi metallic connecting flange is intendedto be fixed to this condenser member at substantially its mid-point andthe lower end of the casing 2 arranged to rest thereon to thusrelatively fix these portions of the apparatus. Since this part of thestructure is well known in the art, it is not completely illustrated, Amore complete showing oi such a structure will be found in my 'copendingapplication, Serial No. 235,611, filed i6 is open as at 22 and thisopening is defined by a vertical cylindrical surface 24.

.Avbase plate 26 is provided with an annular groove 28 which is adaptedto receive a pair of gaskets 30 and 32. These two gaskets may be 'of thewell known construction such that the inner gasket 3.0 is relativelyresilient to supply a sealing action while the outer gasket 32 acts inthe nature of a stop therefor. As is most clearly shown in Fig. 2, thisbase plate 26 is provided with a central aperture through which the stud6 extends and includes inwardly extending spacing fingers 21 forslidably engaging the stud to center itself thereon. The base plate isseated on the upper end surface 34 of the insulating casing 2 with thegaskets 30 and 32 .disposed therebetween to form an air-tight seal inthe manner described above.

A flexible metallic diaphragm 36 is secured to the upper portion of thesurface 24 of the cap as by brazing at 38 and includes a centralaperture which isconsiderably larger than the diameter of the stud 6 toprevent its making contact therewith. The inner edge of this diaphragmis arranged to rest on a raised inner perimetral portion 4|! of the baseplate, which portion is preferably grooved asshown to carry a sealinggasket 4i. It will appear that the outside dimensions of this base plateare such that its outer edge surface makes a sliding fit with thesurface 24 of the cap so that it is movable within the opening therein.

An annular clamping plate 42 includes a downwardly projecting seatportion -44 arranged to contact the upper surface of that portion of theflexible diaphragm which engages the portion 46 of the-base plate. Thisclamping plate is preferably provided with spacing fingers around itsopening similar to those indicated at 21 on the base plate to center itabout the stud in slidable relation thereto. A number of spaceddepressions or seats 46 are formed in the upper surface of this clampingplate to be engaged by bolts 48 forming part of a biasing or clampingassembly.

This clamping assembly includes a fitting 50 which is threaded to theportion ill of the stud 6 and is preferably in the form of a spiderhaving a hole 52 in each of its fingers. In the apparatus shown, foursuch fingers are provided and one of the bolts 48 is loosely disposed ineach of them. An annular plate 54 is provided with bosses 56 spacedsimilarly to the holes 62 and having screw-threaded apertures therein.One of the bolts 48. extends through each of these apertures and ahelical spring 68 surrounds each bolt so as to be compressed between thefitting 60 and plate 54;

It will thus be seen that the bolts 46 exert a downward pressure on theclamping plate 42 which, in turn, pressesdownwardly on the fiexiblediaphragm 36 to seal the joint between this diaphragm and the base plate26. This same pressurealso acts to bias the plate 26 downwardly relativeto the stud 6 to exert a sealing pressure on the gaskets 30 and 32.Thus, with the main portion of the cap rigidly secured to the stud, thebase plate 26 is free to slide longitudinally therein as a result oftemperature changes. At the same time the diaphragm keeps the interiorof the cap sealed despite any such movement.

The method of assembling the above described device will be foundparticularly convenient. After the insulating casing 2 is disposedaround the stud 6, the base plate 26 is centered on the stud and broughtto rest upon the end of the casing. The side wall portion l6 of the capis then placed on the assembly with the flexible diaphragm 36 in itsproper position relative, to

the base plate, after which the interior portions of the cap may beassembled in a manner which will appear evident. The bolts 46 are thenadby means of machine screws 60. With the washers 69 extending past thesurface 24 of the cap portion l6, it will appear that the base platewill act to prevent the portion l6 from moving downwardly during theassembly operation. After the device is assembled the washer 53 andscrew 66 must, of course, be removed.

While the construction described above provides a particularlysatisfactory cap for an insulating bushing, it will, nevertheless,appear that the power factor testing of such a bushing cannot beaccomplished without disconnecting the line from the upper end of thestud 6 and also disconnecting the electrical apparatus being suppliedfrom the lower end thereof. In the modification of the invention shownin Fig. 3 I have provided an arrangement which greatly simplifies thetesting operation.

Referring to Fig. 3, a thin layer 62 of insulating material is disposedon the surface of the stud 6' along the greater portion of its lengthand extends up past the clamping plate 42'. A coating 64 of conductingmaterial is then applied to the surface of this insulating materialwithin the insulating casing 2'. A condenser member 6' which isotherwise similar to that of Fig. 1 is then applied to the stud overthese two coatings.

In this modification, the base plate 26', instead of being completelymetal, is provided with a ring 66 of insulating material such as micartaat its outer edge or perimeter. The ring 66 thus slidably' engages thesurface 24 of the hole in the cap portion l6 to permit the base plateassembly to move relative to the cap. In addition, the

raised portion 40 of this base plate is not grooved as in the previouscase but a gasket member 4|, is disposed thereon between a pair ofnon-compressible insulating gaskets 66 which may, for example, be ofasbestos material. The flexible diaphragm 36' is thus completelyinsulated from the base plate and the stud.

A conducting member I0 is electrically connected to the conductingcoating 64 as by soldering at 12, and serves to electrically connect itto the base plate 26' by meansof a screw I4. .Another flexible conductor16 is secured to the base plate 26' at 18 and is removably attached tothe .cap portion I6 at 60. It will appear that'this conductor 16 willelectrically connect the cap to the conductor member during normaloperation of the bushing. During power factor testing, however, theconductor I6 may be disconnected at 60 and the base plate 26 correctedto the testing apparatus, the other end of which may be secured to themetallic clamping flange. During such testing operation, the cap, studand, consequently the apparatus within the tank are completelydisconnected and thepower factor of the bushing from the conductingcovering 64 may be readily ascertained. If the shielding circuit of thetest set is connected directly to the body of the cap, the difference inpotential between the stud 6 and the bottom plate 26 will be so smallaasaass that the insulation provided by the ring 88 and gaskets 88 willbe ample to withstand it.

From the above description, it will appear that the present inventionprovides an insulating bushing with. a cap structure which isinexpensive to manufacture, simple to install, and which will providemost satisfactory operating properties. In addition, the apparatusmay beeasily dismantled for repairs in the field and readily adapted forconvenient power factor testing.

Since various modifications of the apparatus shown and described indetail will appear to those skilled in the art, it is intended that theinvention will be limited only by the appended claims interpreted inview of the prior art.

I claim as my invention:

1. In a bushing for high tension electrical apparatus including atubular casing of insulating material having a stud extending axiallytherethrough and projecting beyond an end thereof, said stud having aportion thereof fixed with respect to a portion of said casing; a capextending around and secured to th projecting portion of said stud andhaving an open bottom portion, a base plate proportioned to seat on theadjacent end face of said casing and fitting in movable relationshipinto said cap to sub stantially close the open bottom thereof throughouta predetermined range of movement therebetween, a flexible memberdisposed within said cap for sealing the space between it and said baseplate, and means for biasing said base plate against said tubularcasing.

2. In a bushing for high tension electrical apparatus includin a tubularcasing of insulating material having a stud extending axiallytherethrough and projecting beyond an end thereof, said stud having aportion thereof fixed with respect to said casing; a cap extending aboutthe projecting portion of said stud and having an opening defined in itsbottom by a substantially vertical surface portion, means for securingsaid cap to the projecting portion of said stud. a base plate positionedto seat on the adjacent end face of said casing and extending into saidbottom opening in the ca'p, said base plate being of a shape similar toand slightly smaller than said opening and being movable therein tosubstantially close said cap despite relative movement withinpredetermined limits therebetween, a flexible diaphragm sealed to saidcap adjacent the edge of said opening and having its inner edge seatedon a portion of said base plate, and a spring-biased plate member forbiasing said diaphragm against the inner edges of the said base plateand said base plate against said casing.

3. In a bushing for high tension electrical apparatus including atubular casing of insulating material having a stud extending axiallytherethrough and projecting beyond an end thereof. said stud having aportion thereof fixed with respect to said casing; a cap extending aboutthe projecting portion of said stud and having an opening larger thanthe adjacent end face of said casing in the bottom thereof, means forsecuring said cap to said stud, a base plate proportioned to seat onsaid adjacent end face of said casing and extend into said bottomopening in movable relationship to said cap to retain the openingsubstantially closed throughout a predetermined range of movementtherebetween, a flexible diaphragm disposed within said cap for sealingthe bottom thereof between the opening and said base plate, means forresiliently biasing a portion of said diaphragm against said base plateand said base plate against said casing, and means for limiting theextension of said plate into said cap during the assembly of thebushing.

4. In a bushing for'high tension electrical apparatus including atubular casing of insulating material having a stud extending axiallytherethrough and projecting beyond an end thereof, said stud having aportion thereof fixed with respect to said casing; a metallic capextending about the projecting portion of said stud and having in itsbottom an opening larger than the adjacent end face of said casing,means for securing said cap to said stud, a base plate proportioned toseat on the adjacent end face of said casing and extend into said bottomopening in movable relationship to saidcap, said base plate including amain metallic portion with a perimetral portion of insulating materialdisposed adjacent to the surface of said cap to insulate it therefrom,a, flexible metallic diaphragm sealed to said cap and extending to saidplate to seal the space therebetween, insulating means disposed betweensaid diaphragm and said plate to prevent electrical contacttherebetween, means for exerting a sealing pressure on the insulatedjoint between said diaphragm and said plate and on the joint betweensaid plate and said casing, an insulating cover surrounding said studwithin said casing and adjacent said base plate to insulate it from saidbase plate, conducting material surrounding said insulating cover withinsaid casing, electrical conducting means for connecting said plate tosaid conducting material, and readily disconnectable means forelectrically connecting said plate to said cap.

ALEXANDER A. SKVOR'IZOFF.

